The invention relates to a device for determining a shaft center deviation and to a method for determining a shaft center deviation.
Magnetic bearings can be subdivided into passive magnetic bearings and active magnetic bearings. In the case of passive magnetic bearings, use is either made of the repelling or attracting forces which occur between permanent magnets or of the attraction forces between permanent magnets and ferromagnetic materials. In the case of active magnetic bearings, the magnetic field required is generated with the aid of electromagnets. The magnetic field and thus the currently acting forces can be changed by varying the current in the coils of the electromagnets. In order to be able to mount a machine part in such a manner, a control operation which ensures that the currently required bearing forces are available is always required. The controlled variable is the center deviation of the part to be mounted or of the shaft to be mounted. This position is measured in a contactless manner using a sensor.
It is known practice to configure the sensor in such a manner that it comprises a stator into which an excitation winding system is inserted, said winding system being fed with an AC voltage. Part of the shaft to be mounted projects into the stator. Hall sensors introduced into the stator measure the magnetic field and use it to determine the shaft center deviation.
However, the disadvantage is that the Hall sensors are difficult to manufacture and are therefore expensive and that a zero point adjustment operation must take place before the sensor is started. However, under certain circumstances, the zero point adjustment operation must be repeated after a certain operating time since the material of the sensor ages. Accordingly, the use of Hall sensors also results in inaccuracies when determining the shaft center deviation.